The free aqueous phase was obtained from individual samples of dental plaque and the palque matrix was then eluted with a chaotropic buffer in an attempt to remove bound protein. The fluid and the chaotropic phases were assayed for secretory immunoglubulin A (SIgA), IgG, IgM, the third component of complement (C'3), lysozyme, lactoperoxidase and lactoferrin. The presence of these specific and non-specific immune factors in the free and bound phases suggest they are important in host defense at the plaque enamel interface.